The present disclosure herein relates to photomasks. As design rules of semiconductor apparatuses have become smaller, a wavelength of light used in an exposure process has reduced, too. Therefore, extreme ultraviolet (EUV) light having a short wavelength may be used in the exposure process. When mass producing nano-scale semiconductor devices of 40 nanometers (nm) or less, an EUV lithography using EUV light having a wavelength ranging from about 10 to about 14 nm may be used.
When forming a plurality of fine patterns that are arranged at high density by using the EUV lithography process, the EUV light having high energy may be absorbed by an absorber layer of a photomask and may not reach a wafer. Accordingly, research on a technology of transferring patterns on a wafer by using a reflective type exposure system including a reflective EUV photomask has been actively conducted recently. Because of the reflective photomask, patterns on the photomask may be transferred onto the wafer via a scanning process. Therefore, a defect of the photomask may cause a defect of a device formed on the wafer.
In particular, in a case where a registration error occurs on the photomask, a wafer overlay error may occur. Then, the overlay error may be transferred onto the wafer, and a wafer defect may occur.